Cryocooled computers are being used increasingly due to their improved performance. In these computers certain logic components are cryogenically cooled to increase the speed of operation. It is well known in the art to cool these logic components by placing them in direct contact with a cryocooler cold head which is insulated from the external environment usually by being placed in a vacuum vessel. However, it is extremely difficult to maintain the extremely low cryogenic temperatures.
Liquid nitrogen immersion cooling has been widely anticipated for the future. The liquid nitrogen immersion cooling method, provides for a cooling scheme in which a multi-chip module is cooled by direct contact with the cold head, instead of using a cold head of a cryogenic refrigerator to condense nitrogen and achieve low temperatures. This cooling scheme, however, requires a low resistance chip-to-cold plate thermal interface in order to achieve the desired chip operating temperatures. A key problem which still remains is material resiliency which is known to decrease sharply at low temperatures, leaving uncertainty as to the reliability of the thermal joint. If the interface compound should become brittle, for example, thermal stresses can result in cracking and/or separation from the chip or cold plate surfaces causing the joint to fail.
Therefore it is very important to provide mechanical compliance between the chips and the cooling hardware. Today, it is known in the art to insure compliance by placing a piston-like structure that can translate and tilt in a hole over each chip to achieve intimate contact with the back of the chip. Heat that is conducted into the piston is subsequently dissipated through a water or air cooled cold plate. Another mechanical approach that has been used is the radial finger. However, good thermal performance of the chip piston and chip-radial finger interfaces, will only be achieved if the interface is immersed in a media of sufficiently high thermal conductivity and density.
Reduced thermal interface conductance can be achieved at room temperature with helium gas. However, a helium flooded chip-piston interface performs poorly at cryogenic temperatures because the thermal conductivity of helium is much lower at those temperatures than at room temperature.
In addition if a vacuum vessel is used, the added problem of internal pressure controls have to be resolved. Furthermore, the use of a vacuum vessel also adds the problem of passing any electrical cable connected to the components through the sealed vessel.
U.S. Pat. No. 5,121,292 seems to disclose a cryogenic field-replaceable logic unit for use with a cryogenic cold head. In one embodiment, liquid nitrogen is used for immersion cooling of the chips and carrier placed in a vacuum sealed vessel. This embodiment uses a recess to hold a pool of liquid cryocoolant. However, there are no teachings or suggestions of a method using two separate mixtures of condensible and non-condensible gases with the pressure of the non-condensible gas having a partial pressure equal to the desired saturation pressure of the condensible gas as described in the present invention.
U.S. Pat. No. 4,800,422 apparently discloses a double walled vessel having a styrofoam filling between the double walls internally supporting a semiconductor circuit to which a cable ribbon is attached. It seems then that an electrical cable pass-through is produced between the insulated portions of cryogenic cooler used for VLSI testing. There are no teachings or suggestions of a cooling method comprising a mixture of gases above a liquid pool above a cryogenically cooled module or an improved cold plate design as suggested in the present invention.
U.S. Pat. No. 5,142,443 apparently teaches a mounting arrangement for electronic circuit chips in which at least one chip is mounted upon an appropriately electrically insulative chip plate. However, there are no teachings or suggestions of a method using two separate mixtures of condensible and non-condensible gases with pressure with the non-condensible gas having a partial pressure equal to the desired saturation pressure of the condensible gas as described in the present invention.
U.S. Pat. No. 5,050,114 appears to teach a method for predicting the optimum operating conditions for a two-phase liquid cooling environment using simulation software. There are no teachings or suggestions of cryogenic cooling of electronic components using mixtures of two distinct gases.
U.S. Pat. No. 4,647,338 apparently discloses a method of manufacturing through which the partial pressure of a condensible gas in a mixture is maintained with another gas. There are no teachings or suggestions, however, of an improved method of cooling electronic components using a mixture of gases above a liquid pool of cryogenically cooled liquid, or an improved cold plate design as suggested in the present invention.